1. Field of the Invention
The present invention relates generally to power supplies for applications and devices that require small, low-cost, high-voltage power supplies. These power supplies can be used, for example, in high-density and ultra-high-density data storage devices.
2. Description of the Related Art
FIG. 1 illustrates a portion of a Van De Graaf apparatus according to the related art. A Van De Graaf apparatus is typically manufactured on a macroscopic scale and is often used to raise the hair of students during high school science demonstrations as the students touch the apparatus with their hands.
The portion of the apparatus illustrated in FIG. 1 has a charged species source 10 that is connected to an electrical ground 20. In close proximity to the edge or tip of the charged species source 10 is a belt 30 that is wrapped around a first roller 40 and a second roller 50. The belt 30 travels in a closed path around the rollers 40, 50 as the rollers 40, 50 turn or spin about their fixed axes 45, 55.
The first roller 40 is either positively or negatively charged and the second roller 50 either remains uncharged or is oppositely charged relative to the first roller 40. Away from the charged species source 10, but also proximate to the belt 30, is positioned a charged species drain 60. The charged species drain 60 is electrically connected to a device 70 such as a power supply or capacitor. During operation, the Van De Graaf apparatus supplies a current to the device 70.
The charged species source 10 generally is made from a metal or other conductive material. The charged species source 10 generally takes the shape of a pin or a comb. However, other geometries are sometimes used.
The belt 30 is typically made of rubber. The first roller 40 typically is made from a material other than rubber. The second roller 50 is typically made of a material that is neither the material used to make the belt 30 nor the material used to make the first roller 40. However, under certain circumstances, the second roller 50 and the belt 30 are made from the same material.
The charged species drain 60 can be made from a metal or other conducting material. The charged species drain 60 is often in the shape of a pin or a comb, although other geometries are sometimes used. The device 70 to which the charged species drain 60 is electrically connected can be any type of apparatus that would benefit from a high potential current being supplied to it.
When operating the Van De Graaf apparatus, the first roller 40 typically undergoes a charging process. The first roller 40 can be either positively or negatively charged, depending on the type of charged species that are used to supply current to the device 70. For example, if electrons are used, the first roller 40 is positively charged.
In order to charge the first roller 40, charged species may be supplied to the first roller 40 from an outside source. Alternatively, the first roller 40 can be tribocharged.
Tribocharging involves “frictional charging” between two contacting surfaces that are made from different materials. Since different materials attract electrons with different amounts of force, tribocharging operates on the principle that, when two different materials rub against each other, the electrons in the surface atoms of one material will be more strongly attracted to the other material and will effectively “tear off” of one material in order to attach themselves to the other. If the materials continue to rub against each other over time, one material will become more and more negatively charged while the other material will become more and more positively charged as surface atom electrons continue to move from one material to the other.
In FIG. 1, the surfaces of the first roller 40 and of the belt 30 move relative to each other when the first roller 40 turns and moves the belt 30. Also, because the belt 30 and first roller 40 are made from different materials, charged species from the surface of the belt 30 are transferred to the surface of the first roller 40. Therefore, over time the first roller 40 becomes charged. The belt also gets charged, but because it is larger, the charged species are more diffuse.
When it is desirable for the second roller 50 to be oppositely charged relative to the first roller 40, the material from which the second roller 50 is made can be chosen such that, as the surface of the belt 30 moves relative to the second roller 50, tribocharging occurs that is opposite in polarity to the tribocharging that occurs between the first roller 40 and the belt 30. In other words, in FIG. 1, the belt 30 can tribocharge the first roller 40 with one type of charged specie and can charge the second roller 50 with an oppositely charged specie.
When, on the other hand, it is desirable that an uncharged second roller 50 be used, the belt 30 and the second roller 50 can be manufactured from the same material, thereby preventing tribocharging. Also, even if different materials are used to make the belt 30 and second roller 50, the charged species that build up in the second roller 50 can be quickly removed by an external electrical connection.
Once the desired charging has occurred in each of the rollers 40, 50, the charged species source 10 is “turned on” and charged species begin to flow towards the tip of the charged species source 10 closest to the belt 30. The charged species at the tip of the charged species source 10 then get attracted by the charged first roller 40 and travel towards it. However, the charged species do not travel through the belt 30 and therefore effectively become attached to the belt 30.
Once the charged species are attached to the belt 30, the moving belt 30 transports the charged species from a position near the first roller 40 to a position near the oppositely charged or uncharged second roller 50. Once the charged species are near the second roller 50, they either experience no electrostatic forces between themselves and the second roller 50 or experience repulsive electrostatic forces that repel the charged species away from the second roller 50.
The unattracted or repelled charged species them approach the charged species drain 60. When the species get close enough to the drain 60, they move off of the surface of the belt 30, through the drain 60, and to the device 70 where they supply a current at a high electrostatic potential.
The related art device illustrated in FIG. 1 has the disadvantage that it can only be used on a macroscopic scale. Further, a significant amount of energy is required to move the belt 30 by using the first roller 40 and second roller 50.